A day cream is a moisturiser, and the right one depends on your skin type.
How moisturisers work
Humectants draw water into the skin and occlusive ingredients slow water loss. Ointments are more occlusive than creams, and creams more than lotions, so drier skin tends to prefer creams and lighter lotions suit oily skin.
Sunscreen
The NHS recommends SPF 30 or higher with at least 4-star UVA protection. If your day cream lists an SPF, check it meets this and remember that people usually apply less than the amount used in testing.
Patch test
Try new products on a small area first and stop if skin becomes irritated.
Sources: Wikipedia: Moisturizer, NHS: Sunscreen and Wikipedia: Sunscreen.
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